1. Field of Invention
This invention relates generally to the field of oil production and more particularly concerns a method for enhancing recovery of oil from wells.
2. Description of the Prior Art
Roughly half of the energy of the United States comes from oil which is either imported or extracted from domestic sources. Despite long-term increases in oil prices, domestic production of crude oil has declined in the face of stepped-up drilling nationally and the development of the Alaska pipeline. While recent efforts have curtailed U.S. imports, the majority of oil in the United States remains in the ground.
The principle reason this oil has not been recovered is because it is economically difficult to extract due to attractive forces between the oil and the rock formations in which it resides. Van der Waals, surface tension and other inter-molecular attractive forces cause the oil to adhere to the rock. As a result, for every one barrel of oil that is extracted from a well, approximately two barrels remain in the ground. Estimates by the U.S. Department of Energy suggest that 334 billion barrels of oil are in place that are not economically recoverable with conventional technology.
Over the last decade, much research has been conducted into methods of extracting and recovering this oil, and numerous methods of secondary and tertiary recovery have been developed. Among these methods, the simplest technique for enhancing oil recovery is water flooding.
With this technique, a new hole is drilled in the vicinity of a producing well and water is pumped into the formation to provide the necessary pressure to keep oil in the formation flowing toward the producing well. The exact location of the well and the selection of water injection points requires considerable geologic expertise. Approximately 90% of all U.S. oil fields use this technique as a secondary recovery method. However, water alone is not an ideal substance for moving oil through porous rock because water tends to flow through the larger channels in the rock and leave much of the oil in the smaller channels. Because water and oil do not mix, the majority of oil remains adhered to the rock formation.
An alternate method of recovery is known as the "Micellar-Polymer Process" which is an improvement on the water flooding technique that uses detergents and surfactants to reduce the surface tension between water and oil and increase the efficiency of water in driving oil out of the well. Generally a molecule having an organophilic end and a polar end is deployed under pressure throughout the formation. The organophilic end is attracted to the oil while the polar end is attracted to water. The result is that much of the oil is organized into tiny droplets called "micells" which are more easily moved through the rock formation to the producing well. Specially prepared polymer solutions are often injected into the formation to facilitate migration of the oil toward the well. While the micellar process is much more expensive than water-flooding, the enhanced recovery makes the process economically feasible.
Unfortunately, the micellar process is not as effective as desired, and much of the oil remains in the ground adhered to the rock formation.
Carbonation of wells has also been proposed as a method of secondary recovery. In this process carbon dioxide is pressurized into the well, forming a liquid phase which is soluble in oil. The primary disadvantage of this technique is that, like water, liquid CO.sub.2 passes through the formation much more rapidly than the oil and thus carbonation leaves more oil in place than the micellar polymer process. Moreover, this techique is only effective in wells where about 100 billion barrels of oil remain in place. Of this oil, the technique can assist in recovering only about 10%.
All of the processes mentioned above share the disadvantage of leaving much oil adhering to the rock, and the further disadvantage of being ineffective with heavier crudes and tars that are even less mobile than the average crude.
Steam injection techniques have been developed which heat the heavier constituents to increase fluidity. Generally, the pressurized steam is pumped down separate injection wells to facilitate adequate production. Obviously, this method involves drilling several new bore holes into the formation and high energy costs. The method has the added disadvantage that in deeper wells, especially those below 2,500 feet, the steam is too cool to do much good. It has been suggested, however, that this technique could lead to the recovery of an additional 1.6 billion barrels of oil.
Many additives that enhance the recovery of oil have been developed. Several of these are designed for use in conjunction with steam injection and down hole surge tool techniques. Down hole surge tools periodically treat sections of the well bore with pressurized fluid to increase the porosity of the treated sections and thus increase production. The tool is usually used at specific distance intervals in the hole and treats localized areas. However, many of these additives, including silicates, have a tendency to clog the well or to destabilize or decompose under the extreme conditions found in subterranean wells, and are not as effective as desired.
Hence, a process for enhancing secondary and tertiary recovery of oil from wells which does not involve substantial expense, which appreciably increases oil production and which employs relatively stable compositions having good shelf life qualities and capable of remaining stable under the conditions found in subterranean wells is both economically and politically desirable.